Electronic timer



April 2 T. A. BIRCKHEAD ELECTRONIC TIMER Filed May 20, 1950 WITN ESSES:

a INVENTOR 70 I Taylor A.B|rckheod.

TORNEY Patented Apr. 22, 1952 ELECTRONIC TIMER Taylor A. Birckhead, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 20, 1950, Serial No. 163,257

4 Claims. 1

My invention relates to electrical apparatus and more particularly to electronic timer circuits.

Many manufacturing processes include certain operations which require timing of closely related cycles. In some operations where a material is to be welded or clamped, heated, cooled and released, the time intervals involved may be of the order of fractions of seconds. The total time of the operation as well as the ratio of the various time intervals is often critical. Electronic timers are peculiarly well adapted for timing these operations.

In accordance with the teaching of the prior art of which I am aware, a separate electronic timer has been used to time each cycle of an operation. For example, suppose a particular operation requires a material to be clamped, welded or heated, cooled and released. In accordance with the teachings of the prior art separate timers are provided for the heating and the cooling times. Each of these timers includes an electric discharge device with an associated time constant network. A separate control is provided to adjust the time of each cycle. Such a timer, because of the duplication of discharge devices and other components for each timing cycle is necessarily costly. In addition, each component of a timer contributes a certain proba-- bility of failure and a certain complexity in finding cause of failure. It is, therefore, desirable that the number of components be minimized.

It is an object of my invention to provide an improved two-cycle electronic timer.

Another object of my invention is to provide a two-cycle electronic timer which is characterized by its simplicity of operation, compactness of structure and economy of manufacture.

It is another object of my invention to provide an electronic timer which utilizes only one electric discharge device to produce two consecutive timed cycles.

It is another object of my invention to provide anpelectronic timing control circuit for use in apparatus in which a material is to be clamped, welded or heated, cooled, and released, which control circuit shall utilize a single electric discharge device, and shall include means for clamping said material at the beginning of the heating, or welding, time and for releasing the material at the end of the cooling time.

It is a further object of my invention to provide a two-cycle timer in which the ratio of the two cycles can be adjusted by a single control.

It is a further object of my invention to provide a two-cycle timer in which the total length 2 of the two cycles can be adjusted by a single control.

In accordance with my invention, I provide a circuit including an electric discharge device having at least an anode, a cathode and a control electrode. A pair of timing networks, each including resistive and reactive elements, are connected in the control circuit of said discharge device. Suitable means are provided "to initiate operation of the first timing network to produce a first timed interval, which is terminated by conduction of said discharge device. Operation of the second timing network to produce a second timed interval, is initiated responsive to conduction of said discharge device. This second timed interval i terminated by cut-off of said discharge device. The timing networks are so arranged that one variable resistance determines the ratio of the timed intervals, and another variable resistance determines the total length of the timed intervals. Thus a single electric discharge device is utilized to produce two consecutive timed cycles.

Other objects and advantages of my invention will appear from the following description when read in connection with the accompanying drawing, in which the single figure is a schematic diagram showing a preferred embodiment of my invention. 7

Referring in detail to the drawing, a pres in which material to be heated may be placed is indicated generally at H. The press comprises a stationary member [3 and a movable member l5. One member contains a suitable heating element shown for convenience as a resistor l1 supplied from the secondary winding [9 of a transformer 2| whose primary winding i connected in series with a contact 23 of the heating relay 25 across the buses 21, 29 of a commercial power source (not shown). The movable element of the press may be operated by an air solenoid or a hydraulic device, or any suitable means, but for convenience is shown being operated by the armature of a press relay 3!. The energizing coil 33 of the press relay 31 is connected in series with a start switch 35 across the power supply buses 21, 29.

A timer network indicated generally at 31 includes a single electric discharge device which may be a thyratron 39 having an anode M, a cathode 43 and a control element 45. A cathode 43 of this thyratron 39 is connected to one of the power supply buses 21 and the anode M is connected through a, resistance 41 and the operating coil 49 of the cool relay 5| to the other power supply bus 29. A smoothing capacitor 53 is connected across this resistance 41 and the cool relay operating coil 49. The smoothing capacitor 53 and resistance 51 could be replaced by a small selenium rectifier if desired. The usual stabilizing capacitor 55 is connected from the thyratron control element 45 to its cathode 43.

The timer circuit includes a capacitor 5'! for timing heat time and a capacitor 59 for timing 0001 time. The heat time'capacitor 51 is connected from the thyratron cathode 53 through first normally closed contacts 6| of the cool relay 5| and a bias resistance 63 to the thyratron control element 45. The cool time capacitor 59 is connected from the thyratron cathode 53 through first normally open contacts 55 of .the cool time relay 5| and the bias resistance 63 to the thyratron control element 55. The cool time capacitor 59 is shunted by second normally closed contacts B1 of the cool time relay 5!. A dropping resistance 59 is connected in series with a ratio potentiometer ll across the power supply buses 27, 29. The heat time capacitor 51 is charged by a circuit which may be traced from the movable element 53 of the ratio potentiometer ll through a rectifier '35, a resistance Ti and normally closed contacts i9 of the heat relay through the heat time capacitor 51 to the power supply bus 2?. The discharge circuit of the heat time capacitor 57 may be traced from a power supply bus 2? through second normally closed contacts 5? or the cool relay 5|, a resistance 8! and a total time potentiometer 93 through the heat time capacitor 5'land back to the power supply bus 27. The cool time capacitor 59 is charged by a circuit which may be traced from the mov able element Til-of the ratio potentiometer H through the rectifier l5, resistance ll, normally closed contacts i9 of the heat relay 25, total time potentiometer 83, resistance 5|, the cool time capacitor 59 to bus 2']. Thus, the discharge resistances Si, 83 of the heat time capacitor 51' are the charge resistors of the cool time capacitor 59. The energizing circuit for the heat time relay coil 85 may be traced from one power supply bus 21 through the normally open contacts 89 of the press relay 3| through the heat relay coil 85 and third normally closed contacts 55 of the cool relay 5| and the start switch to the other power supply bus 29. The start switch 55 is shunted by second normally open contacts 53 of the cool relay 5|. The start switch is also shunted by second normally open contacts 95 of the heat relay 25.

The start switch 35 is closed to initiate an operation. The press relay coil 33 is energized closing the press I i and the normally open contact 89 of the press relay 3!. The operating coil 85 of the heat relay 25 is now energized and its first normally open contacts 25 close the heating circuit while its second normally open contacts 95 lock the start switch 35 in, and its first normally closed contacts 79 open the charging circuit of the heat time capacitor 51. The heat time capacitor begins to discharge through the total time potentiometer 55, a resistance 5| and the second normally closed contacts 57 of the cool relay 5|. When the heat time capacitor 5'! has discharged surficiently, the thyratron becomes conductive and energ zes the cool time relay 5|. First normally closed contacts 5| of the cool time relay 5| remove the heat time capacitor 57 from the thyratron bias circuit while first normally open contacts 65 of the cool time relay 5| place the .0001 time capacitor 59 in the thyratron bias circuit, and second normally closed contacts 57 of the 0001 time relay 5| remove the shunt from the cool time capacitor 59. Third normally closed contacts 9| of the cool time relay 5| deenergize the heat relay 25 and open the press heating circuit. The start switch lock previously provided by second normally open contacts 95 of the heat relay 25 is now provided by second normally open contacts 93 of the cool relay 5|. Normally closed contacts 19 of theheat relay 25 energize the charging circuit for the cool time capacitor 59. When the cool time capacitor 59 has charged sufficiently, the thyratron 39 is cut off to deenergize the cool time relay 5|. Contacts 93 of the cool time relay 5| open, deenergizing the operating coil 33 of the press relay 3|, which in turn opens the press H for removal of material. Heat time capacitor is fully charged and connested in the grid circuit of the discharge device 39, and the cool time capacitor is discharged through the shunt contacts 61 of the cool time relay 5 l. The circuit is now set for another operation.

The heating time is determined by the length of. time it takes the heat time capacitor 57 to discharge through the total time potentiometer and resistor 8|, while the cool time is determined by the length of time it takes the cool time capacitor 59 to charge through the total time potentiometer and the resistor 8|. Adjustment of the ratio potentiometer if to increase the charge on the heat time capacitor 51 and thus increase the heat time will also increase the charging rate of the cool time capacitor 59 and decrease the cool time. The ratio potentiometer then comprises a single control for adjusting the ratio or heat time to cool time. Adjustment of the total time potentiometer 83 to decrease the discharge rate of the heat time capacitor 57 to increase the heat time will also decrease the charging rate of the cool time capacitor59 and increase the cool time. The total time potentiometer 83 then is a single control for adjusting the heat and cool time together and thus the total time of the operation.

While I have described the two-cycle timer of .iy invention as being used in connection with a heating operation, it is apparent that it could be applied to other operations which involve pairs of closely related timed cycles.

In a system in accordance with my invention which was constructed and successfully operated. the following components were included:

Capacitor 59 1 microfarad Capacitor 5i 1 microfarad Capacitor 55 .002 microfarad Potentiometer 83 0-5 megohms Potentioineter l! 0-10,000 ohms Resistance Tl 12,000ohms Resistance 65 3L3 megohms Resistance ill 0.2 megohm Resistance 59 47,200 ohms Discharge device 39 Type 2050'thyratron I am aware that certain modifications of my invention will appear to those skilled in the art.

'I therefore desire that my invention be restricted only insofar as is necessitated by the prior art and the spirit of the appended claims.

1 claim as my invention:

1. In com ination, an electric discharge device 7 having an anode, a cathode, and a control electrode, a first capacitor connected in series with first normally closed contacts and said control electrode, a second capacitor connected in series with normally opensecondcontacts and said control electrode, third normally closed contacts connected in shunt with said second capacitor, charging means connected in series with fourth normally closed contacts across said first capacitor and in series with said fourth contacts and a resistance across said second capacitor, means to effect opening said fourth contacts whereby said first capacitance discharges through said resistance and said discharge device is rendered conductive, means responsive to conduction of said discharge device to actuate said first, second, and third contacts and to effect closing of said fourth contacts, whereby said first capacitor is disconnected from said control element, and said second capacitor is connected to said control electrode and its shunt removed and said charging means is effective to charge said second capacitor through said resistance to render said discharge device non-conductive.

2. In combination, an electric discharge device in an initial state with reference to conduction, a first network comprising a first capacitor for timing a first interval, a second network comprising a second capacitor for timing a second interval, a common source of potential for charging said capacitors, means to vary the magnitude of said charging potential, means to actuate said first network to initiate the timing of said first interval, means operative upon expiration of said first interval to render said discharge device in the opposite conductive state, means responsive to the change in conductive state in said discharge device for initiating said second timing interval, and means responsive to expiration of said second interval to render said discharge device in said initial conductive state.

3. In combination, an electric discharge device in an initial state with reference to conduction, a first network comprising a first capacitor for timing a first interval, a second network comprising a second capacitor for timing asecond interval, a common source of potential for charging said capacitors, means to vary the magnitude of said charging potential, a variable resistance common to the discharging circuit of said first capacitor and the charging circuit of said second capacitor, means to actuate said first network to initiate the timing of said first interval, means operative upon expiration of said first interval to render said discharge device in the opposite conductive state, means responsive to the change in conductive state in said discharge device for initiating said second timing interval, and means responsive to expiration of said second interval to render said discharge device in said initial conductive state.

4. In combination, a first relay, switch means for momentarily causing energization of said first relay, a second relay, first contacts actuable responsive to energization of said first relay to cause energization of said second relay, second contacts actuable responsive to energization of said second relay to shunt said switch means, an electric discharge device having an anode, a third relay having energizing means connected in circuit with said anode, third and fourth. contacts actuable responsive to a change in the state of conduction of said discharge device, said third contacts being connected to shunt said switch means, and said fourth contacts being connected to cause deenergization of said second relay.

TAYLOR A. BIRCKI-IEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

